1. Field of the Invention
The present general inventive concept relates to a hard disc drive (HDD), and more particularly, to a HDD having improved head stability at low temperatures, and a method of supplying current to a head of an HDD.
2. Description of the Related Art
Generally, hard disc drives (HDDs) are recording apparatuses used to store digitally encoded data. Typically, the data is recorded on concentric tracks that are formed on a surface of a magnetic recording disc. The magnetic recording disc is rotatably mounted on a spindle motor, and the data is recorded on the concentric tracks are accessed by a read/write head that is mounted on an actuator arm. The actuator arm is rotated by a voice coil motor and is actuated by a current supplied from the voice coil motor. With regard to the read operation of the read/write head, a current is supplied to the read/write head to record data on the magnetic disc. The supplied current generates a magnetic field, and the magnetic field magnetizes the surface of the magnetic recording disc. The read/write head reads the data that is recorded on the surface of the magnetic recording disc by detecting magnetic changes within the magnetic disc.
Various improvements have been made to HDD read/write heads, including separating out the read device (or read head) from the write device (or write head). The separate read device utilizes the magneto resistance (MR) effect, which changes the resistance of a material in the presence of a magnetic field. With the advent of increased storage capacity of HDDs, the conventional giant magneto resistance (GMR) read head was introduced. However, it has been discovered that the GMR head does not provide sufficient bit per inch (BPI) read sensitivity. Therefore, most of the present HDDs generally use a tunnel magneto resistance (TuMR) head as the read operation head. In contrast to the GMR head, the TuMR head has a high BPI read sensitivity, and is very stable and reliable at high temperatures. The enhanced BPI sensitivity, stability and reliability of the TuMR head during read operations can be attributed to the fact that the TuMR head draws less current, as compared to the GMR head, when a read operation is performed. However, the read operation of the TuMR head is unstable at low temperatures since the TuMR head is made of a thin film. Therefore, the instability of the TuMR head at low temperatures has been evaluated by using various test methods. One test method includes supplying a current to the TuMR head that is much greater than the current supplied in a normal read operation. In other words, the instability of the TuMR head at low temperatures is pre-tested by performing a read operation under severe conditions. An alternate method of testing the read operation at low temperatures includes placing a TuMR head directly in a low temperature chamber. However, with both scenarios catastrophic problems may arise. For example, due to the excessive current supplied to the TuMR head in the first test scenario or alternatively, due to the large current required to drive the HDD in the second test scenario, the TuMR head can be damaged. Therefore, there still exists a need to effectively address the instability of the TuMR head during a read operation at low temperatures.